1. Field of the Invention
This invention generally relates to a shock absorber having a piston rod which is guided therein by a one-piece sheet metal piston rod guide. Such a shock absorber can possibly have, among other things, a sealed cylindrical tube, which can be an outer tube thereof, and an inner, concentrically disposed pressure tube that can preferably be filled with damping medium. The space between the sealed cylindrical tube and the pressure tube can typically form an equalization chamber, and a piston rod gasket can close the shock absorber from the atmosphere. The sheet metal guide can typically comprise a graduated, circular, pot-shaped base body with a concentric guide surface for a bearing bush, a contact surface for the piston rod gasket and a guide surface in relation to the sealed cylindrical tube. There can also be at least one reflux opening for passage of damping fluid therethrough from an area above the guide back into the equalization chamber.
2. Background Information
In a general type of piston-cylinder arrangement, such as a shock absorber, damping medium, which can be oil, can leak between the piston rod and the guide. Also, on the other hand, gas can repeatedly collect in the pressure tube. The leaking damping medium and the collected gas are typically discharged back into the equalization chamber by means of the piston rod guide complex. This discharge back into the equalization chamber prevents the piston rod gasket from being pressurized by the high damping pressure, or from causing malfunctions and rattling noises as a result of the presence of gas in the high-pressure portion.
On shock absorbers of this type which are subjected to severe stresses, it is also conventional to gas-pressurize the shock absorber, to improve their functioning. This gas pressure promotes the gravity actuation of the shock absorber and suppresses the tendency to foaming. So that the gas does not escape into the atmosphere via the piston rod gasket, such a shock absorber can also contain a gas lock. The gas lock is, in practical terms, a smooth-running rubber hose valve, which provides that the piston rod gasket is fully immersed in the damping medium (oil), and that when the shock absorber is stationary, the gas no longer has any access to this space, from which it could escape to the outside via the piston rod surface. By using high-quality, but also expensive, gasket materials, it even becomes possible to eliminate the gas lock altogether in some cases. Generally, the piston rod guides have been made from a rigid suspension part, which is usually manufactured of sintered metal or similar moldable materials (die cast aluminum, die cast zinc).
One problem with the manufacture of these parts by sintering or molding, is always the deformability of the complicated reflux openings, i.e. undesirable burrs are formed during the manufacturing process. If these burrs are machined out, then undesirable particles of dirt can get into the damping medium, which in turn has an adverse effect on the function of the damping valves. Deburring, e.g. by means of spot sandblasting, makes the already expensive part even more expensive.
The disadvantages which result from the use of sintered material for a piston rod guide can be reduced by using a sheet metal piston rod guide. German Laid Open Patent Application DE-OS 40 30 788, for example, discloses a one-piece sheet metal piston rod guide, but the piston rod guide described therein also has several disadvantages.
One primary point of criticism for this known guide assembly, is the large amount of space occupied in the axial direction of the shock absorber. Thus, because of the excess axial length, the useful stroke length of the shock absorber is significantly reduced, and if a decompression stop pad is also used, the axial stroke length can be even further reduced.
An additional disadvantage is that, as a result of the orientation of the piston rod gasket in relation to the piston rod guide, an axial misalignment can occur, so that the piston rod seal does not perform a uniform sealing function.
Also, the danger of foaming in the equalization chamber is increased by the disadvantageous positioning of the reflux openings, which positioning allows the damping medium to fall unobstructed into the equalization chamber. Further, the known arrangement of DE-OS 40 30 788 also does not provide any measures which exert a prestress on the shock absorber to prevent the above-mentioned internal leaks.